Communication system



June 6, 1944.

H. SALINGER COMMUNICATION SYSTEM Filgd Oct. 25, 1941 FlG.l

2 Sheets-Sheet l souRcE OF RADIO FREQUENCY CARRIER SIGNAL FIG.2

SIGNAL REPRODUCER INVENTOR SAL|NGER In. a! A ATTORNEY June 6, 1944. sALlNGER 2,350,331

COMMUNI CATION SYSTEM Filed Oct. 25, 1941 2 Sheets-Sheet 2 SIGNAL REPRODUCER 246 0 PHASE OSHIFTERG Patented June 6, 1944 COMLIUNICATION SYSTEM Hans Salinger, Fort Wayne, Ind; assignor to Farnsworth Television andRadi'o Corporation, W a corporation of Delaware Application October 25, 1941, Serial No. 416,429

7 Claims.

This invention relates to a wireless communication system for transmitting and receiving telegraph signals, such as are used in the transmission of code or picture telegraphy and more particularly relates to a new system of transmission which has a certain degree of secrecy.

In conventional communication systems for transmission of code signals or in picture telegraphy systems, it is usual to transmit, alternately,- a carrier signal of constant amplitude and frequency and no signal. The intervals of carrier signal transmission and non-transmission thereof, respectively, are representative of signal units of different character in the signal to be transmitted. In a telegraph code signal, the dots and dashes each comprise predetermined numbers of marking units, while the spaces between dots and dashes comprise predetermined numbers of spacing units. In picture telegraphy, the marking units may represent light portions of the picture to be transmitted, while the spacing units may represent dark portions of the picture, or vice versa. It is evident that, in any type of transmission, the energy transmitted must have two different characteristics in order to be representative of signal units of different, character.

In many cases, it is desirable to effect secret communication, that is, to employ a type of transmission which can only be received by a particular receiver. Systems in which unauthorized reception is made practically impossible are very complicated, while a lesser degree of secrecy often fulfills the requirements.

It is the object of the present invention. therefore, to provide a simple new system of wireless communication, having a certain degree of secrecy without necessitating the complicated arrangements of conventional secret communication systems.

According to the invention, there is provided a communication system for transmitting and receiving telegraph signals comprising units of difi'erent character including a transmitter and a receiver. The transmitter includes a plurality of transmitting antenna elements and means for successively applying predetermined potentials to these antenna elements to produce waves of energy in space, having a circular polarization of predetermined rotation for transmitting signal units of one character. Means are also provided for changing the order in which the potentials are applied to the antenna elements to produce waves of energy in space having a circular polarization with the opposite direction of rotation for transmitting signal units of another character. The system includes a receiver comprising a. plurality of receiving antennae for intercepting the transmitted waves of energy. The receiver also comprises means coupled to the receiving antennae'for superimposing the energy waves successively intercepted by the receiving antennae in such manner that energy waves transmitted with one of said directions of rotation are superimposed in aiding relationship, thereby to obtain resultant signal units of different character, dependent on the direction of rotation of the intercepted waves.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 is a circuit diagram of a transmitter embodying the present invention;

Fig. 2 shows a receiver for receiving waves transmitted by the transmitter of. Fig. 1; and

Figs. '3 and 4 show a modified transmitter and receiver, respectively, also embodying the present invention.

Referring now more particularly to Fig. 1 of the drawings, there is shown schematically a transmitter comprising a source of radio frequency carrier signal I, whose output circuit is connected to the input circuits of three amplifiers 2, 3 and 4, respectively. Each of the amplifiers 2, 3 and t has two tubes connected in push-pull relation. Amplifier 2 is provided with a tuned resonant output circuit 5, while amplifiers 3 and 4 are provided with a common tuned resonant output circuit 6. For radiating the radio frequency signal into space, there is provided a dipole antenna T, 1, coupled by means of a line 8 and an inductance coupling means 9 to the output circuit 5 of the carrier signal amplifier 2. For transmitting circularly polarized waves of energy, there is provided a second dipole antenna l0, l0, arranged in radial formation with the dipole antenna I, I and being displaced with respect thereto by substantially as shown. The dipole antenna I 0, III is coupled by way of a line H, a. 90 phase shifter i2 of conventional design and an inductance coupling element I 3 to the common output circuit 6 of the radio frequency signal amplifiers 3 and 4.

For changing the direction of rotation of the circularly polarized waves of energy radiated into space by means of the antennae l, l and I0, I ll, there is provided a keying arrangement amplifier 4 and ground, and asecond biasing arrangement comprising a resistor I! and a battery I8 connected in series relation between the cathodes of amplifier tubes of amplifier 3 and ground, as shownr The biasing voltage produced by the battery I 3 is of a magnitudesuitable for proper operation of the amplifier 4, while the i biasing voltage produced by the battery I8 is of a magnitude to bias the tubes of amplifier 3 to current cut-oil. For changing the biasing voltages for the cathodes of the tubes of amplifiers 3 and 4, and thereby rendering amplifier 3 inactive and amplifier 4 active, there is further pro,-

vided a battery 23 and a grid-controlled electron discharge tube I 9 connected in series relation between the cathodes of the tubes of amplifiers 3 and 4, respectively, as shown. For controlling the operation of discharge tube I9 and, thereby, also the, operation of amplifiers 3 and 4, respectively, there is provided "a' key or switch 20, a biasing battery 2| and a resistor 22, all connected in series relation, the terminals of resistor 22 being connected between the control grid and the cathode of discharge tube I3;

In operation, the source of radio frequency carrier signal I produces a carrier signal which is applied to the input circuits of amplifiers 2, 3 and 4, respectively. In the condition of the circuit shown, with switch 23- open, amplifier 3-is active while amplifier 4 is cut off, as will be explained below. Radio frequency signals amplified by the amplifier 2, appearing in the output circuit 5, are applied by way of coupling element 9 and line 3 to the dipole antenna I, I, whereby the polarity of the waves of energy radiated by each of the elements I, I is 180 out of phase. The carrier signal from the source I applied to the input circuit of amplifier 3 and appearing in the output 6 is applied by way of the inductance coupling element iii to the 90 phase shifter I2, in which the phase of the signal is shifted through an angle-of substantially 90. The phase-shifted signal is then applied by way of line It to the dipole I0, I0 and the waves of energy radiated 'into space by each of the elements of the antenna I 0, III are 180 out of phase with respect to each other and 90 out of of battery l8, which makes the cathodes of the tubes of amplifier 3-negative, thus rendering this amplifier active. when the switch 23 is closed, a voltage dropacross the resistor 22 is produced by means of .a. battery 2|, which renders tube I9 nonconducting. Therefore, the

terclockwise direction of rotation of the circularly polarized waves radiated therefrom to 'a clockwise rotation.

If the switch or key 20 is operated in accord- V ance with code signals comprising marking units,

such as dots and dashes and spacing units consisting of the intervals the rebetween,-the character of these'units is distinguished by the different directions ,of rotation of the circularly polarized waves radiated by the antennae I, I

and I0, ill. Obviously, the key 20 and battery 2| phase with respect to the waves radiated by the circularly polarized waves of energy having a counterclockwise direction of rotation are radiated by the antennae I, I and ill, I B.

In the condition of the circuit as shown, tube I3 is operated substantially at zero bias and a current flows from ground through battery I8. resistor I'I, tube I9, battery 23, resistor 45 and battery It to ground. In this case, a voltage drop is developed across resistor I5, counteracting the voltage of battery I6, which makes the cathodes of the tubes of amplifier 3 positive. thus cutting off this amplifier, and a voltage drop is developed across resistor fll, counteracting the voltage phase delay by passing throu h phase shifter I2,

can be replaced by other means adapted to apply a control signal to the tube l3, which may, for example, berepresentative of dark and light picture elements, respectively, of an image to be transmitted, as is conventional practice in the art of picture telegraphy.

Fig. 2 shows a receiver adapted to receive and reproduce the signals transmitted by the transmitter of Fig. 1. This receiver comprises a first dipole antenna 30, 33 provided for intercepting the waves of energy radiated by the antennae I, I and I0, ill of the transmitter of Fig. 1. Antenna 30, 30 is coupled to a radio frequency amplifier 3| of conventional construction for amplification of the intercepted waves. For further amplification of the waves, there is provided an amplifier 32 comprising two tubes connected in push-pull relation, as shown, and having a tuned resonant output circuit 33.

There is also provided'a second dipole antenna 34, 34 coupled to a second radio frequency amplifier 35 of conventional design. The output of this amplifier, which may be .of, identical design as amplifier 3|, is coupled to a phase shifter 36, preferably a phase delay network, which retards the phase of the received waves by The phase-shifted waves are then applied to an amr' plifier 31 comprising two tubes connected in push-pull relation and having a tuned resonant output circuit 38. A signal reproducer, schematically indicated at 33, is coupled to the output circuits 33 and 33 of amplifiers 32 and 31, respectively, by meansof an inductance coupling member 40. The signal reproducer 33 is of any suitable conventional design and may comprise a conventional detector and tape recorder or buzzer for reception of code signals, or may include a glow lamp and scanning apparatus in.

the case of picture telegraphy.

In operation, circularly polarized waves of energy are intercepted by the antennae 30, 33 and 34, 34 and amplified by radio frequency amplifiers 3| and 35, respectively. The output signals of amplifier 3| are further amplified by amplifier 32 to produce an amplifiedsignal in the output circuit 33. The output signal of the amplifier 35 is delayed in phase through an angle Of s b tantially 90 by the phase shifter 33 before application to the amplifier 31, by means of which amplified signals are develope in the output circuit 38. The output signals appearing in the output circuits 33 and 36 are superimposed in the coupling element 40.

For a counterclockwise direction of rotation of the circularly polarized waves of energy intercepted by the antennae 30, and 34, 34, the output signals of radio frequency amplifier 3| and are 90 out of phase, whereby the output signals of amplifier 3| will lead the output signals of amplifier 35 by 90. Since the phase shifter ,36 introduces an additional lagging phase of 90, in the waves intercepted by antenna 34, 34, the output signals developed in the output circuits 33 and 38 become 180 out of phase and, therefore,

no signal is developed in the coupling element 40. If, now, the direction of rotation of the circularly polarized waves intercepted by the antenna is changed to a clockwise direction, the output signals of amplifier 35 lead those of amplifier 3| by a phase angle of 90. This leading phase is annulled bythe 90 phase delay produced by the phase shifter 36. The output signals in the output circuits 33 and 38 are then in aiding-phase relation and a signal is developed in the coupling element 40 and applied to the signal reproducer 39. In this manner, resultant signal units of different character are obtained; in this particular case, units of signal or no-signal,

dependent on the direction of rotation of the circularly polarized waves intercepted by the receiver antennae.

Fig. 3 shows a modified transmitter using phase shifts of 20 instead of 90 and comprising three grid-controlled electron discharge tubes 4|, 42 and 43, whose cathodes are connected together. Each of the tubes is provided with a tuned output circuit 44, 45 and 46, respectively. The inductance element of each of the output circuits 44, 45 and 46 is provided with a tap which is coupled to phase shifters 41, 48 and 49, respectively. These phase shifters are preferably delay networks of conventional design and capable of delaying the phase of an applied voltage by an angle of 60. The output of each of the phase shifters 41, 48 and 48 is connected to the control grid of the following tube, so that energy from the output circuit 44 of tube 4| is delayed in phase by an angle of 60 by phase shifter 41 and applied to the control grid of tube 42. Likewise, energy from the output circuit 45 of tube 42 is delayed by an angle of 60 by phase shifter 48 and applied to the control grid of tube 43. Finally, energy from the output circuit 46 of tube 43 is shifted through an angle of 60 by the phase shifter 49 and applied to the control grid of tube 4| in the condition of the circuit, as shown. This provides a system with positive feed-back, which is capable of generating self-oscillations and represents the source of radio frequency carrier signals.

. For the purpose of radiating circularly polarized waves of energy, there are provided three antennae 5|, 53 and 55, arranged in radial formation, forming angles of 120 between each other. The direction of rotation of the circularly polarized waves depends upon the order in which the antennae are successively energized, or, in

' other words, the respective phases of the energy supplied thereto. For energizing the antennae, output circuit 44 of tube 4| is inductively coupled by means of an inductive coupling element 50 to antenna 5|. Likewise, output circuit 45 of tube 42 is inductively coupled by means of a coupling element 52 to antenna 53. Finally, the output circuit 46 of tube 43 is inductively coupled by means of a coupling element 54 to antenna 55.

For changing the direction of rotation of the circularly polarized waves, there are provided three switches 56, 51 and 58, each having two positions. In the position shown in solid lines, energy from the output circuit 44 of the tube 4| is supplied to the control grid of tube 42, after being delayed by 60. Hence, the phase of the output signal of tube 42 lags that of tube 4| by an a gle of 240, taking into consideration the phase r versal by 180 due to tube 4|.

Energy from the output circuit 45 of tube 42 is supplied to the control grid of tube 43, after being delayed by 60 by the phase shifter 48. Hence, the phase of the output signal of tube 43 ljagsliglaat of tube 42 by 240, and that of tube 4| 3' waves of energy are radiated by the antennae 5|, g3 and 55, having a clockwise direction of rota- If, now, the switches 56, 51 and 58 are brought into the position indicated by the dotted lines. energy from the output circuit 44 of tube 4| is applied, after passing through phase shifter 41, to the control grid of tube 43, and energy from the output circuit 46 of this tube is applied, after passing through phase shifter 49, to the input of tube 42. Finally, energy from the output circuit 45 of tube 42 is passed through phase shifter 48 and applied to the control grid of tube 4|. It is evident, therefore, that the output signal in output circuit 44 leads that in output circuit 46 by 240 and that in output circuit 45 by 480. In this manner, the order in which antennae 5|, 53 and 55 are energized has been changed and, hence, also the direction of rotation of the circularly polarized waves radiated therefrom has been changed to a counterclockwise direction.

Switches 56, 51 and 58 can be mechanically combined into one unit so that there is provided a single switching means which may consist of a manual switch or key or of a relay. Actuation of the key or relay may be effected in accordance with code signals or picture signals, as may be the case.

Fig. 4 shows a receiver for receiving and reproducing the signals transmitted by circularly polarized waves. This receiver comprises three antennae 60, 6| and 62, arranged in radial formation and forming angles of 120 therebetween. For amplifying the waves of energy intercepted by the antenna 60, there is provided an amplifier generally indicated at 63, whose input circuit is inductively coupled to the antenna 60 by means of a coupling arrangement 64. For amplifying the waves of energy intercepted by the antenna 6| there is provided an ampl fier generally indicated at E5, to whose output circuit is coupled antenna 6| by means of a phase shifter 66, prefera-bly a phase delay network of conventional design, capable of developing a 120 phase delay and a coupling arrangement 61. For amplifying the waves intercepted by the antenna 62, there is provided an amplifier generally indicated at 68 coupled to the antenna 62 by means of a 240 phase shifter 69 of conventional design, capable of producing a 240 phase delay and a coupling arrangement 10. Each of the amplifiers 63, 65 and 68 is provided with inductance elements 1|, 12 and 13 in their respective output circuits, across which amplified signals are developed. Coupled to the inductance elements'1l, 12 and 13 is an inductance coupling element 14, in which the signals amplified by the amplifiers 63, 65 and In this manner, circularly polarized tively.

08 are combined into a single signal; The inductance coupling element leis coupled to a'signal reproducer 15, of suitable conventionaldesign which, again, may include a detector and tape recorder or buzzer for reception of code signals or which may include a glow lamp and scanning apparatus for picture -teleg'raphy. In operation, the antennae 60, 68 and 62 may be assumed to intercept circularly polarized waves having acounterclockwise direction of rotation so that the energy supplied to the coupling element 64 leads that supplied to coupling element 6! by 120 and that supplied to coupling element 10 by 240. The waves interceptedby antenna 60 are appliedto the amplifier 63 without phase delay and an amplified signal is developed across the inductance element H and the amplifier output circuit. The waves applied to the coupling element 61 already lag the waves applied to coupling element 64 by 120 and'are subjected to an additional 120 phase shift in the phase shifter 66, so that the amplified signals developed across the inductance element 12 and the output circuit of the. amplifier 65 lag' the signals in element II by 240. The waves intercepted by antenna 62 and applied to the coupling element I lag the waves intercepted by antenna 60 by 240 and are subjected to an additional 240 phase shift in the phase shifter 69 so that the amplified signals developed across the element 13 in the output circuit of the amplifier 68 have a lagging phase of, 480 with respect to the signals developed across element II. If three sinusoidal signals, of which the second lags the first in phase by 240, while the third lags the first by 480 are vectorially added, it is found that the three signals compensate each other at all times since the phase angles are equivalent to angles of 0, 120 and 240 degrees. Therefore, no signal is inducedin the coupling element I4, which could be applied to the signal reproducer 15.

If, now, the direction of rotation of the circularly polarized waves intercepted by the antenna is reversed so that the waves intercepted by antenna 62 lead those intercepted by antenna 60 I Hence, also with the transmitter of Fig. 3 and receiver of Fig. 4'resultant signals are obtained; in this particular case, units qt signal or no-signal, dependent on the-direction of rotation of the circularly polarized waves intercepted by'the receiver antenna.

Since the receiver required for reception of circularly polarized waves diiiers considerably from conventional receivers, a certain degree of secrecy is inherent in the described system.

' With the particular antenna arrangements shown, a high degree of directivity is obtained which is favorable for point-to-point communication.

While there has been-described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within'the truespirit andv scope of the invention.

What is claimed is: I

1. Apparatus for transmitting telegraph signals comprising units of different character which comprise a plurality of antenna elements. a source of radio frequency carrier signals, means for applying carrier signals toone of said ele- ;direction of rotation for transmitting units oi one character, a second repeating means coupled between said source of radio frequency carrier signals and said other element forapplying said signals to said other element and changing the phase of said signals to produce waves having a circularpolarization with the opposite direction of rotation for transmitting units of another character and means for rendering either said first repeating means or said second repeating means effective for applying said radio frequency carrier signals to said other element.

2. Apparatus for transmitting telegraph signals comprising units of difierent character which comprises a first antenna, a source of radio frequency carrier signals, means for'applying carrier signals to the, elements of said antenna whereby to radiate signals of a certain phase, a

second antenna the elements of which are displaced with respect tolithe elements of said first antenna, a first repeating means coupled between said source of radio frequency carrier signals and said second antenna for applying said signal to said second antenna with a certain phase difference with respect to signals applied to said first antenna to produce waves of energy inspace rier signals to said second antenna.

3. Apparatus for transmitting telegraph signals comprising units of different character which comprises a plurality of antenna elements, means for applying carrier'signals to one of said antenna elements whereby to radiate waves of energy. a second means coupled to another of said antenna elements for applying signals to said other antenna elements with a phase diflerence with 'respect to signals applied to said one antenna element such as to produce waves of energy in space having a circular polarization of predetermined direction of rotation for transmitting units of one character, a third means for applying signals to said antenna and changing the phase of said signals to produce waves having a circular polarmeans for rendering either said second means or said third means efiective for applying signals to said antenna.

4. Apparatus for transmitting telegraph signals comprising units of difierent character which comprises a first dipole antenna, a source of radio frequency carrier signals, means for applying carrier signals to the elements of said antenna whereby the polarity of waves of energy radiated by each of said elements is 180 out of phase, a second dipole antenna the elements of which are displaced by substantially 90 with respect to the elements of said first antenna, a first repeating means coupled between said source of radio frequency carrier signals and said second antenna for applying said signals to said second antenna with a phase difference of substantially 90 with respect to signals applied to said first antenna to produce waves of energy in space having a circular polarization of predetermined direction oi. rotation for transmitting units of one character, a second repeating means coupled between said source of radio frequency carrier signals and said second antenna for applying said signals to said second antenna and changing the phase of said signals by substantially 180 to produce waves having a circular polarization with the opposite direction of rotation for transmitting units ofanother character and means for rendering either said first repeating means or said second repeating means eilective for applying said radio frequency carrier signals to said second antenna.

5. Apparatus for receiving telegraph signals comprising units of difierent character transmitted by means of waves of energy radiated in the space, said waves being circularly polarized with difierent directions of rotation representing said different character of said signal units, which comprises a plurality of antenna elements arranged in radial formation to intercept said waves, means for superimposing the energy waves intercepted by said antenna elements, a first signal repeating means coupled between one of said antenna elements and said superimposing means, and a second signal repeating means including phase-shifting means connected between other of said antenna elements and said energy superimposing means thereby to reproduce telegraph signals comprising units of different character dependent upon the direction of rotation of the intercepted waves.

6. Apparatus for receiving telegraph signals comprising units of different character transmitted by means of waves of energy radiated in the space. said waves being circumrly polarized with different directions of rotation representing said different character of said signal units, which comprises a plurality of antenna elements arranged to intercept said waves, means for combining the waves intercepted by said antenna elements comprising a pair of primary windings and a secondary winding, a first signal repeating means coupled between one of said antenna elements and one of said primary windings, and a second signal repeating means including phaseshifting means connected between another of said antenna elements and the other of said primary windings, thereby to reproduce telegraph signals comprising units of different character dependent upon the direction of rotation of the intercepted wave.

'7. A communication system or transmitting and receiving telegraph signals comprising units of different character which comprises a first antenna, a source of radio frequency carrier signals, means for applying carrier signals to the elements of said antenna whereby to radiate signals of a certain phase, a second antenna the elements of which are displaced with respect to the elements of said first antenna, a first repeating means coupled between said source of radio frequency carrier signals and said second antenna for applying said signals to said second antenna with a certain phase difierence with respect to signals applied to said first antenna to produce waves of energy in space having a circular polarization of predetermined direction of rotation for transmitting units of one character, a second repeating means coupled between said source of radio frequency carrier signals and said second antenna for applying said signals to said second antenna and changing the phase of said signals to produce waves having a circular polarization with the opposite direction of rotation for transmitting units of another character and means for rendering either said first repeating means or said second repeating means eiiective for applying said radio frequency carrier signals to said second antenna, and a receiver including a plurality of antenna elements arranged in radial formation to intercept said Waves, means for superimposing the energy waves intercepted by said antenna elements, a first repeating means coupled between one of said antenna elements and said superimposing means, and a second signal repeating means including phase-shifting means connected between other of said antenna element and said energy superimposing means thereby to reproduce telegraph signals comprising units of different character dependent upon the direction of rotation of the intercepted waves.

HANS SALINGER. 

